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Chapter 7. Electro-organic chemistry

 

作者: R. Lines,  

 

期刊: Annual Reports Section "B" (Organic Chemistry)  (RSC Available online 1977)
卷期: Volume 74, issue 1  

页码: 153-163

 

ISSN:0069-3030

 

年代: 1977

 

DOI:10.1039/OC9777400153

 

出版商: RSC

 

数据来源: RSC

 

摘要:

7 Electro-organic Chemistry By R. LINES Laboratory of Organic Chemistry The Norwegian Institute of Technology The University of Trondheim N- 7034 Trondheim NTH Norway 1 Introduction The current state and growth of electrosynthetic chemistry together with an outline of the most promising reactions of recent years is the subject of a Russian review.' Another Russian paper2 surveys current problems in the anodic fluorination of organic compounds. On the cathodic side a useful review3 written from a physical- organic standpoint has appeared concerning the electroreduction of organic compounds both in aprotic and aqueous media. 2 Anodic Processes The Anodic Oxidation of Carboxy1ates.-Alkyl benzenes are reported4 to be obtained in good yield by the Kolbe electrolysis of 1-alkyl- 1,4-dihydrobenzoic acids.Thus decarboxylation of (1)offers a useful synthetic route to the 1-alkyl naphthalenes. (1) A systematic study5 of the migratory aptitudes of the alkyl substituents (R' or R2) in the oxidation of P-hydroxy carboxylic acids (2; R3= H) revealed preferential migration of olefinic cyclopropyl or benzylic groups. OH 0 0 -2e II II R'R2CkHR3COZH -R2CCHR'R3+R1CCHR2R3 -C02/-H20 (2) Scheme 1 ' M. Ya. Fioshin Soviet Electrochem. 1977 13 1. I. N. Rozhkov Russ. Chem. Rev. 1977,45615. P. J. Elving Canad. J. Chem. 1977 55 3392. J. Slobbe J.C.S. Chem. Comm. 1977,82. ' T. Shono J. Hayashi H. Omoto and Y. Matsumura Tetrahedron Letters 1977,31 2667. 153 154 R. Lines When R3=Me however the selectivity was much diminished reflecting the importance of the conformation of the intermediate carbenium ion.The results of the study were applied to the synthesis of dl-muscone (4)via the olefinic acid methyl ester (3) (Scheme 2). 0 HO ,CH2C0,Me II The electrolysis of acylaminomalonic acid monoesters6 in acetic acid solutions has been found to produce a good yield of the useful synthetic intermediates 2-acetoxy-2-amino acid derivatives. Similarly the 3-acetoxy-3-amino acid deriva- tives were obtained from the oxidation of 3-alkoxycarbonylalanine derivatives in acetic acid-THF media. Anodic oxidation of 4,4-diphenyl but-3-enoic acid' (5; R =H) in methanol results in a readily separable mixture of isomeric diphenyl ally1 ethers (6,7; R' = H R2=Me).Similarly electrolysis of the Stobbe half-ester (5; R = C02Et) in ethanol yields the corresponding esters (6,7; R' = CO,Et R2=Et). R2 Ph HRPh CH2CO2- -2e MeOH or EtOH Ph Ph 0 R' +%HR1 Ph CH2OR' Ph (51 (6) (7) Scheme 3 The relative simplicity of the electrochemical route compared with the alter- native chemical syntheses makes this an attractive method for the preparation of these compounds. The Anodic Oxidation of Neutral Organic Compounds.-The anodic chemistry of the tropane alkaloids has been studied' in both acetonitrile and benzonitrile. Controlled potential electrolysis of tropane (8; R =Me) in acetonitrile results in the uptake of 0.79Fmol-' to yield a mixture of (protonated) tropane (57.6'/0) nortropane (8; R = H 13.6%) and the N-carboxaldehyde (8; R = CHO 5.3%).Both nortropane and the N-carboxaldehyde are believed' to be derived from the iminium ion (9). The aldehyde is the major product in the presence of hydroxide. R\ (8) (9) (10) CH2* NRQ/N-ND T. Iwasaki. H. Horikawa K. Matsumoto and M. Miyoshi J. Org. Chem. 1977,42 2419. 'F. M. Banda and R. Brettle J.C.S. Perkin f 1977 1773. B. L. Laube M. R. Asirvatham and C. K. Mann J. Org. Chem. 1977,42,670. Elec tro -organic Chemistry 155 The oxidation of nortropane results in the formation of both C-N (8;R = CH2CN) and N-N bonds (10). The cyanide is thought to arise from generation of solvent radicals formed from the oxidation of hydroxide ions. OH-CH3CN -e CH2CN+H20 Scheme 4 This is supported by the observation that binortropane (10) is the major product in benzonitrile where solvent radical formation is prevented.The anodic cyanation of t-aliphatic and heterocyclic amines has been the subject of a systematic study.' Preparative electrolysis of the amines at Pt in aqueous methanolic sodium cyanide solution yielded a-cyan0 amines in reasonable yields (30-60%). The ease of cyanation was found to be in the order (CH,) >(CH2)5>Me >Et >Pr" >Pr' = 0. This reactivity series was rationalized' by consideration of the geometry of the amine on the electrode surface. Deprotonation the key step in the reaction must occur at the a-carbon situated in a position easily accessible to the electrode. Obviously this is not the case for the isopropyl group.Similarly the configuration of the adsorbed cyclic amines encourages substitution at the a-ring-carbon and for N-isopropylpiperidine ring substitution was the sole reaction. The chemistry of the anodic oxidation of cyclohexene in the presence of cyanide ion turns out to be rather complex.'o In methanolic sodium cyanide solution at Pt not only cyanation but also methoxylation and isocyanation were observed. The isocyanation reaction was highly potential dependent. It is interesting to note that only tarry products were formed when the electrolyses were performed in acetoni- trile. Anodic cyanation reactions carried out in emulsion systems are claimed to give superior results over the more conventional solvent supporting electrolyte combinations.Eberson and HelgCe" now have demonstrated the synthetic utility of emulsion electrolysis for the preparation of 4-alkoxy-4-cyano-biphenyls;a class of liquid crystals. The electrochemical method using aqueous sodium cyanide dichloromethane and tetra n-butylammonium sulphate gave at least a four-fold yield increase over the alternative five-step chemical synthesis. A new mode of oxidative coupling of substituted bibenzyls has been reported." Anodic oxidation of (11;Z = 0)was expected to yield the aporphine skeleton whereas in acetonitrile the bridged lactone (12) was isolated. The mechanism is thought to involve formation of a cation radical in ring a followed by proton loss from the 4-position of the isochromanone ring. Further oxidation of the resulting radical to the cation then serves as an electrophile towards the veratryl ring to give (12).In acidic solution (CH2Cl-TFA) where proton loss is inhibited the spirodienone (13; 33%) is formed. A rather rare example of ortho-coupled biphenyl^'^ results from the controlled potential electrolysis of methoxylated aryl benzoates. The biphenyls are obtained T. Chiba and Y. Takata J. Org. Chem. 1977,42 2973. K. Yoshida T. Kanbe andT. Fueno J. Org. Chem. 1977,42 2313. L.Eberson and B. Helgke Actu Chem. Scund. 1977,B31,813. I. W.Elliott jun. J. Org. Chem. 1977,42 1090. M. Sainsbury and J. Wyatt J. C.S. Perkin I 1977 1750. 156 R. Lines Meorno Me0 OMe Z= 0or NMe (11) OMe (13) in high yield after the passage of 1Fmol-’. Further oxidation results in ortho- and para-quinones.An interesting detail here is that the products can be accounted for by a 2Fmol-’ scheme whereas experimentally 3Fmol-’ is needed for quinone formation. A useful synthetic route to 5,5’-disubstituted hydruillic acids (15) is reported14 from the controlled potential oxidation of 5-alkyl substituted barbituric acids (14) at a pyrolitic graphite electrode (Scheme 5). (14) R’ R2 = H or Me R3= Me Et or PhCH2 Scheme 5 Examination of the 1-methyl and 1,3-dimethyl barbituric acids over the pH range 0-13 revealed much more complex behaviour. l5 Formation of hydruillic acid (15; R3= H) remains the primary process but further oxidation at the 5-position and subsequent reaction with the parent molecule (or the anion at pH> pK,) yields an open chain trirner which by further oxidation finally gives a cyclic trimer.The first example of the electrochemical difunctionalization of saturated hydro- carbons has appeared.16 Anodic oxidation of adamantane in TFA at the potential of the second wave gives after workup adamantane-l,3-diol (70%). Similarly NN’-adamantane- 1,3-diyl bisacetamide (58%) results from oxidation in acetoni- trile. These two nucleophilic solvents are particularly suitable for the high anodic S. Kato and G. Dryhurst J. Electroanalyt. Chem. Interfacial Electrochem. 1977 79 391. l5 S. Kato and G. Dryhurst J. Electroanalyt. Chem. Interfacial Electrochem. 1977 80 181. l6 A. Bewick G. J. Edwards S. R. Jones and J. M. Mellor J. C. S. Perkin I 1977 1831.Electro-organic Chemistry potentials required Extension of the method to non-bridged hydrocarbons where concomitant olefin formation becomes important may require even more efficient nucleophiles to trap the reaction intermediates. A novel combination of light and electrochemistry has been used to effect the oxidation of organic c~mpounds.~’ A catalytic amount of a quinone is irradiated in the presence of the substrate and a graphite anode at the potential of the quinone- hydroquinone couple. The photochemical reaction produces the oxidized substrate together with the hydroquinone which is electrochemically reconverted into the quinone. Last year’s report [Ann. Reports (B) 1976,73 1431 cited the slow intramolecu- lar coupling of the dication of the [2,2]metacyclophane (16; R=OMe).In a voltammetric study of a series of alkylated [2,2]metacyclophanes Sat0 and Kamada18 suggest the involvement of a transannular cation radical of the 5,13-dimethyl derivative (17). R -@-R __ -(16) (17) Preparative electrolyses of (16; R = H or Me) resulted” in successive oxidation deprotonation reactions to give ultimately the corresponding pyrenes. The dications of the tetrathioethylenes (18; n = 2 or 3) generated in acetonitrile undergo a novel endocyclic to exocyclic rearrangementlg (Scheme 6). Rotation about the central C-C bond of the product provides the driving force of the rearrangement by minimizing the coulombic repulsion between the positive sulphur atoms. The mechanism is ~uggested’~ to be a simultaneous intramolecular migration of two u bonds an example of a dynotropic rearrangement.This same rearrangement reaction characterizes the anodic chemistry of the ortho-thio-oxalates*’ of type (19) (Scheme 7). An interesting feature is that (20) is not the primary product of the rearrangement of the cation of (19). Both the pyrolysis and photolysis of (19) give (20) directly which suggests that the electrochemical frag- mentation is directed by conformational and/or solvation effects. ” J. M. Bobbitt and J. P. Willis J. Org. Chem. 1977 42 2347. T. Sat0 and M. Kamada J. C. S. Perkin II 1977,384. l9 R.M. Harnden P. R. Moses and J. Q. Chambers J. C. S. Chem. Comm. 1977,11. ’* P. R.Moses R. M. Harnden and J. Q. Chambers J. Electroanalyt.Chem. Interfacial Electrochem. 1977,84 187. 158 R. Lines -e -e -e *-LL 77 Scheme 7 3 Cathodic Processes The Cathodic Reduction of Organic Cations.-A new class of stable cation radicals has been prepared2’ by reduction of the diphosphiacyclohexadiene salts (21; R # H). Further reduction yields the highly reactive diphosphabenzenes (22). The cation radicals are unusual in that they decompose by protonation in the presence of strong acids; a property no doubt arising from the strong carbanionic nature of the ring-carbons. Ph ,Ph Ph ,Ph Ph ,Ph +e SH 7 L -+ products Jr’r” RP R Ph/ ‘Ph Ph/ \Ph Scheme 8 The Cathodic Reduction of Neutral Organic Compounds.-Electrogenerated nitrobenzene anion radical in DMF is reported by Wagenknecht22 to react rapidly with alkyl halides to give high yields of NO-dialkylphenyl hydroxylamines.Another useful synthesis involves the electrochemical reductive acylation of electron-deficient ole fin^.'^ Reduction of ethyl cinnamate at a Hg cathode in DMF containing acetic anhydride gave ethyl 3-phenyl-4-oxopentanoate (75%) and ethyl 2-benzyl-3-oxobutanoate (2%). Anthracene however under similar conditions gives the vinyl ester (23) in 66-75% yield.24 The reductive coupling of anthracene with 1,2-and 1,3-dihalide~~~ has been shown by cyclic voltammetry to proceed catalytically. Coupling of the 1,3-dihaIides 21 R. D. Rieke R. A. Copenhafer C. K. White A. Aguiar J. C. Williams jun. and M. S. Chattha J. Amer. Chem. SOC.,1977 99 6656.22 J. H. Wagenknecht J. Org. Chem. 1977,42 1836. 23 H. Lund and C. Degrand Tetrahedron Letters 1977,40 3593. 24 H. Lund Acta Chem. Scand. 1977 B31.424. 2 25 E. Hobolth and H. Lund Acta Chem. Scand. 1977 B31,395. Electro -organic Chemistry 159 in the 1-or 2-positions of anthracene results in ring-closure to cyclo-pentanoanthracene derivatives (Scheme 9). &&, n=7-8 + / + Br(CH2),Br -\\ \\ / Scheme 9 The corresponding catalytic reductive alkylation of quinolines and isoquinolines with t-butyl halides leads to t-butylated heterocyclic compounds.26 A large percentage of the alkylation takes place in the carbocyclic ring. Although many isomers are formed and the overall yield of each isomer is low (10-20°/0) the method has the advantage of experimental simplicity.Electroreduction of halides continues to provide interesting chemistry. The tetra-bromo compound (24) exhibits two major voltammetric peaks.27 Electrolysis at the first wave consumed 3F mol-' and yielded 1,2-dibromobenzocyclobutene and polymers. It was deduced27 that the parent compound (24) is an equilibrium mixture of two conformers and that each product could be ascribed to a single conformer. Reduction of (24) at the second wave gave the tetracyclic product (25) the result of a rearrangement of the Diels-Alder benzocyclobutadiene dimer (Scheme 10). Scheme 10 The as yet unreported dimethylene cyclopropanone (27) is cited 28 as an inter- mediate in the electrolysis of the a,a '-dibromoketone (26).Electroreduction of the readily accessible 2,2,2-trichloroethanol~~~ offers a direct route to 1,l-dichloro-olefins (Scheme 12). Care must be taken to ensure an acidic solution otherwise the alcohol is the sole product. 26 C. Degrand and H. Lund Acta Chem. Scand. 1977 B31,593. 27 L. Rampazzo A. Inesi and R. M. Bettolo J. Electroanalyt. Chem. Interfacial Electrochem. 1977 83 341. L. Rampazzo A. Inesi and A. Zeppa J. Electroanalyt. Chem. Interfacial Electrochem. 1977 76 175. 29 A. Men Angew. Chem. Znternat. Edn. 1977,16,57. 160 R. Lines OH OH R'R2(!XC13 A R'R2C = CCI2 +R'R2LCHCl2 Reagents i Hg cathode 95% EtOH-Et3NHCI Scheme 12 A re-examination3* of cathodic nucleophilic substitution of p-bromobenzo-phenone [Ann. Reports (B),1974 713 2261 has led to the conclusion that the process proceeds exclusively via a bimolecular radical chain-mechanism.A.c. polarographic measurements as well as careful electrolytic experiments showed that the alternative exchange-current pathway could account for only 2% of the total products. The revised mechanism is shown in Scheme 13. (28)+ (30) + PhCOC6H4SPh+(29) (4) (30)+$ [PhC(OH)C6ff4SPh]2 (5) Scheme 13 The same authors31 have presented an efficient method for the electropinacol- ization of ketones. The process involves the use of tetra-alkylammonium salts in carefully dried acetonitrile. Under these aprotic conditions the tetra-alkylam- monium ions are thought to form tight ion-pairs with the ketyl anion radicals and allow dimerization while inhibiting further charge transfer.It is arguedY3' by consideration of the mechanism given in Scheme 13 that the pinacol is essentially a termination product and therefore pinacolization occurs in bulk solution remote from the electrode surface. Pinacol formation characterizes the primary step in the reductive coupling of 1,3-diket0nes.~~ The pinacol from 1,3-diphenyl propane-1,3-dione (31; R = H) is unstable in acidic solution and cyclizes to (32) and a tricyclotrioxanonane (33). Reduction of the corresponding substituted phenyl derivatives (3 1; R = halogen Me or OMe) leads to hexadienediones which can be further reduced to hexene- diones. Compound (33) is thought to result from the dl form of the intermediate pinacol by a double intramolecular ketalization followed by dehydration.Ph OH OH 0 pcOph p-RC6H4 uC6H,R-p ph;;&ph (31) OH (33) (32) 30 W. J. M. van Tilborg C. J. Smit and J. J. Scheele Tetrahedron Letters 1977 24 2113. 31 W. J. M. van Tilborg and C. J. Smit TefruhedronLetters 1977.41 3651. 32 A. J. Klein and D. H. Evans I.Org. Chem. 1977,42,2560. Electro -organic Chemistry 161 A new hydrogen anode33 [Ann. Reports (B) 1974 71 2281 of composite construction has been evaluated and although more efficient than its predecessors the maximum current density and life-time are still limited and need to be improved for more widespread use. An interesting example of conformational effects on fragmentation patterns has been noted in the cathodic cleavage of methyl o-alkyl substituted aryl ~ulphones.~~ Phenyl methyl sulphone is known to undergo exclusive methyl-sulphur cleavage but the introduction of ortho-substituents promotes aryl-sulphonyl fission and this becomes the major mode with the ortho-t-butyl substituted compound.Aryl- sulphonyl cleavage is characteristic of the cyclic aryl sulphones and comparison with molecular models that the conformation of the ortho-substituted sulphones approached that of the cyclic compounds. The electrochemical behaviour of DL-a-lipoic acid3' (a co-factor for a number of enzyme catalysed reactions) has been studied in order to gain some insight into its biological redox mechanism. The oxidized acid (34)cannot be reduced in water but undergoes direct reduction to the dianion in acetonitrile at -1.92 V (SCE)-an extremely negative potential.The acid is however readily reduced by elec- trochemically generated hydrogen which strongly suggests that reduction of the disulphide linkage occurs by an atom transfer-mechanism. (34) '* (34)' Scheme 14 Martigny and Sim~net~~ have devised an autocatalysed cathodic elimination using cY,a'-disubstituted 1,2-diphenyl ethanes. Reduction of (35) in DMF gives a product (trans -stilbene) which is more easily reduced than the parent. The rela- tively stabIe stilbene anion radical then undergoes a homogeneous electron- exchange with the parent molecule. Voltammetric evidence for this process includes a dramatic decay of Ep when the sweep rate is decreased. At very slow scans the Ep of stilbene is reached.PhCH(SPh)CH(O Ac)Ph (35) Labelling experiments often reveal new features of seemingly straightforward reactions. One example is the reduction of phenacyl chloride3' in DMF-l0/' D20. Recovery of the starting material after short reaction-times reveals not only the reduction product (acetophenone) but also considerable H-D exchange of the methylene hydrogens of the starting material. 33 C. P. Andrieux J. M. Dumas-Bouchiai and J. M. Saveant J. Electroanalyt. Chem. Interfacial Elec- trochem. 1977,83 355. 34 B. Lamm and K. Ankner Acta Chem. Scad. 1977 B31,375. 35 J. K. Howie J. J. Houts and D. T. Sawyer J. Amer. Chem. SOC. 1977,99 6323. 36 P. Martigny and J. Simonet J. Electroanalyt. Chem. Interfacial Electrochem. 1977 81 407.37 A. F. Diaz Y. Y. Cheng and M. Ochoa J. Amer. Chem. SOC.,1977,99,6319. 162 R. Lines Interestingly the fraction of phenacyl chloride converted into acetophenone is always less than the fraction of D incorporated into the methylene hydrogens and that the exchange is in excess of the Faraday consumption. A suggestion3' is that the exchange proceeds (at potentials2Ep of phenacyl chloride) via an anion radical which can undergo several H/D exchanges per electron transfer. Falsig and Iversen3* have scaled up the electrolytic reduction of benzotriazole to provide preparative quantities of 2-aminophenyl hydrazine dihydrochloride in 80-85% yields. Treatment of the product with ortho-esters represents a good synthetic route to the 3-substituted benzo-1,2,4-triazines.Evidence has been for the intermediacy of a carbene anion radical during the electrolysis of diphenyldiazomethane. The three isolated products diphenyl methane benzophenoneazine and diphenylmethylamine are believed to arise by a radical-chain process involving the diphenyl carbene radical anion. The observed properties of this species indicates that it behaves primarily as a radical. Although the cation radical of chlorophyll-a is stable in aprotic solvents pre- paration of stable solutions of the corresponding anionic species has proved elusive. A report has now appeared4' that in DMF which has been treated with active alumina both the anion radical and dianion of chlorophyll-a are quite stable. Chemiluminescence has also been observed4' from the reaction of the radical anion with oxygen.The electroreduction of phenylglyoxylic acid oxime in the presence of strychnine leads to opically active phenyl gly~ine,~~ the absolute configuration of which depends on the cathode potential. Thus 17.1% of the R isomer is formed at -0.95 V (SCE) whereas at -1.35 V an enantiomeric excess (1l.lY0) of the S isomer is obtained. Although many different parameters are involved the main factor is probably the protonation of the intermediate chiral carbanion (36) or (37). The product arising as a competition between inversion of the carbanion and protonation in the initial configuration at the electrode surface. PhcC02H PhCCOzH I NHOH I NH2 (36) (37) 4 Miscellaneous The use of minute working electrodes has made possible voltammetric studies in both benzene and chl~robenzene.~~ Chlorobenzene in particular appears to be an excellent solvent for the study of the redox behaviour of aromatic compounds.In benzene the very strong ion-pairing effect allows the reversible formation of the trianion radical of 1,2-bis-(9-anthryl) ethane. The potential (ca. -2.8 V SCE) required to generate this species is the most negative reversible reduction-potential yet reported for an aromatic system. In contrast a report has now appeared43 38 M. Falsig and P. E. Iversen Acta Chem. Scand. 1977 B31 15. 39 R.N. McDonald J. R. January K. J. Borhani andM. D. Hawley J. Amer. Chem. Soc. 1977,99,1268. 40 T. Saji and A. J. Bard J. Amer. Chem. Soc.1977,99 2235. 4' M. Tubault E. Raoult J. Armand and L. Boulares J. C. S. Chem. Comm. 1977 250. 42 R. Lines and V. D. Parker Actu Chem. Scand. 1977 B31 369. 43 M.Horner and S. Hunig Angew. Chem. Internat. Edn. 1977 16,410. Electro -organic Chemistry concerning r-system (38) which can exist in five oxidation states separated by four reversible one-electron transfers. R R (38) 0ther reports have described similar behaviour for two cluster compounds a and a new Pt tetrathiolene clu~ter.'~ tetrameric cyclopentadienyl iron ~ulphide~~ Oxydipropionitrile (dielectric constant = 60) commonly used as a g.1.c. phase shows promise as an electrochemical All the usual supporting elec- trolytes are soluble and at Pt using LiCIO the potential range is +2.62 to -3.9 V (SCE).The Ag/Ag' reference electrode is stable in this solvent. An interesting application of cyclic voltammetry to conformational analysis has appea~ed.~' The technique requires that the conformers be separated by significant activation barriers as well as oxidizing (or reducing) at substantially different rates. Excellent agreement was obtained between the results of low-temperature cyclic voltammetry of cyclic tetra-alkylhydrazines with the known conformational data of these compounds. The authors4' point out that for reproducible results a consistent electrode surface is required. Dia~~~ has noted some differences in stability of some surface bonded pyrazoline derivatives (39) and (40). Both compounds undergo reversible one-electron trans- fer in acetonitrile (X = OMe) but when bonded to the electrode surface (SnOz uia the silylanyl derivative) the charge transfer process becomes irreversible for (40) but not for (39).The conclusion is that the array of cation radicals bonded to the surface are less stable than in solution but that the structure of the tricyclic derivative (39) inhibits decomposition. Ph Ph Strong surface interactions with ions in the electrolyte phase characterize the behaviour of the anisotropic metallic conductor polymeric sulphur nitride (SN), when used as an electrode.49 The electrodes also exhibit unusual heterogeneous electrode process properties. The suggest that such electrodes might be more suitable for modification (chemical or electrochemical) for the fabrication of selective catalysts than for example SnOz or graphite electrodes.44 Trinh-Toan Boon-Keng Teo J. A. Ferguson T. J. Meyer and L. F. Dahl J. Amer. Chem. SOC.,1977 99,408. Boon-Keng Teo F. Wudl J. H. Marshall and A. Kruger J. Amer. Chem. SOC.,1977,99 2349. 46 J. Y. Gal and M. Persin J. Electroanalyt. Chem. Interfacial Electrochem. 1977 77,361. 47 S. F. Nelsen L. Echegoyen E. L. Clennan D. H. Evans and D. A. Corrigan J. Amer. Chem. SOC. 1977,99 1130. 48 A. Diaz J. Amer. Chem. SOC.,1977,99 5838. 49 R. J. Nowak H. B. Mark jun. A. G. MacDiarmid and D. Weber J. C. S. Chem. Comm. 1977 9.

 



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